Broaching may be defined as the cutting away of metal from a part by passing a series of individual cutting teeth mounted on a powered machine slide over the part, each with a progressively deeper cut until the desired depth of cut is obtained.
When broaching for the full length of a part, there is no problem of chip removal since the chips will drop off the part as a tooth reaches the end. However, when the cut is to end midway of the part, the chip remains attached at its uncut root. The removal of the chip has required a second operation either before or after the broach. Preferably, in the past, a relief groove has been cut in the part at the terminal area of the cut and this has, in a sense, provided a false end area where the chips break away and fall from the part. In other cases, the chips could be removed by a subsequent cutting transverse to the broaching direction. In either case, the second operation was time consuming and thus added expense as well as possibly weakening the part by the groove formation. In some cases in a balind hole the chips, still attached at their root, were packed into the base of the hole and left to remain there. The latter method is quite obviously undesirable since some chips might break away and the base of the hole could not be a clean finished surface.
It is an object of the present invention to provide a broaching method which can terminate midway of a part and obtain removal of the rooted chips without the need for an undercut or relief groove.
The invention is directed to a method of broaching forms, either internal or external, on parts requiring the form to run from one edge (point of origin) to an area of permissible cutter generation run but without a separate relief or other operation for chip removal. This method is an alternate machining operation for more conventional machining methods, such as milling and hobbing, both of which utilize circular generating runout areas as the cutter leaves the workpiece.
The method has particular application to the cutting of splines or longitudinal serrations or shafts, both internal and external, but has the advantage that it is not limited to concentric or uniform shapes. It is also applicable to parts which are formed of a material which is of a machinable nature such as would be required for milling or hobbing.
It is desirable that the starting surface, for example, the major diameter of the area to be cut on an external shaft, be held to a tolerance of not more than 0.005", and that this surface extends beyond the runout area for a distance sufficient to accept the total accumulation heights of the chips or curls generated in the completed broaching operation. The cutting is accomplished in the usual broaching concept using a series of individual tooth cutters one following the other in each broaching pass.
Thus, the advantages of a broaching approach to metal removal may be utilized in the removal of metal, such as automatic operations, adaptability to irregular shapes, internal as well as external operations while achieving the necessary chip removal from an uninterrupted surface.
Other objects and features of the invention will be apparent in the following description and claims in which the invention is described together with a disclosure directed to persons skilled in the art to enable the practice of the invention, all in connection with the best mode presently contemplated for the invention.